Materials Literature
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Theoretical study of the vanadyl-oxygen vacancy in V2O5: tight-binding Green function calculation, optical properties and neutral vacancy ground-state splitting, W Lambrecht, B Djafari-Rouhani, J Vennik
An electron diffraction and imaging study of charge-density-wave phases in 1T-VSe2 is presented. Two phase transitions are found. At 110K a 3q-state is formed which at 80K transforms into an irregular pattern of 2q-domains. A Landau theory of these transitions is presented. In order to explain the 3q-2q transition six…
The light scattering and electro-optic response of new material with display potential are investigated. The materials consist of microdroplets of nematic liquid crystals which are spontaneously formed in a solid polymer at the time of its polymerization. Droplet size, spacing, and distribution are readily controlled…
Some liquid-crystalline phases of optically active materials are themselves optically active and have dissymmetric structures. The cholesteric phase and smectics C,I, and F have a helical order of their molecules. Plane-polarized light is rotated by the helix, and when the pitch of the helix is comparable to the wavel…
This paper comprises studies of: the variation of dielectric constant and lattice parameters with temperature using 'single crystals'; the effects on both of different annealing times; variation with annealing times of order, as deduced from the intensities of superlattice reflections, and of Kanzig region size, as de…
Abstract. Titaniuni and its alloys have many applications in aerospace, marine and other engineering industries. Titanium requires special melting techniques because of its high reactivity at elevated temperatures and needs special mould materials and methods for castings. This paper reviews the development of titaniu…
Influence of microstructures in titanium alloys on the basic parameters of deformation behaviour such as slip character, slip length and slip intensity have been explored. Commercial titanium alloys contain the hexagonal close packed (alpha) and body centred cubic (bita) phases. Slip in these individual phases is show…
The electrical conductivity σDC is measured of the glasses in the system x Fe2O3 PbO · 2 B2O3 where x, in moles, varies from 0.1 to 0.6. The conductivity in the temperature region 100 to 350 K follows an expected Arrhenius type behaviour with a slight curvature in ln σ vs. 1/T curves for glasses with x ≦ 0.4. The nove…
Computer simulation of the temperature, dose, and trap filling effects of transient RIC is carried out by means of the Rose-Fowler-Vaisberg formalism. These combined effects allow to determine the trap distribution type exponential or Gaussian, an available data favouring the former. It is also shown that the usual Ro…
Dielectric properties of hexagonal ferrites BaFe12O19, BaTi2Fe4O11, and BaSn2Fe4O11 are examined from 4.2 to 500 K. BaFe12O19 shows low dielectric constant and conductivity, while BaTi2Fe4O11 shows large dielectric constant and conductivity. On the other hand BaSn2Fe4O11 which has the same crystal structure as BaTi2Fe…
At low temperatures the compounds Bi2WO6 and Bi2MoO6, like many other related layered ferro-electrics, are electrically polar and transform to nonpolar state on heating. These phase transitions, however, are not ordinary ferroelectric ones and have a reconstructive nature. The two compounds undergo also additional pha…
Measurements have been made of Raman scattering from pure single crystals of NaCl at several temperatures in the range 300--1025 K. With reference to the 2TA(X) and 2LA(X) bands, which are well resolved at all temperatures, it has been found that the observed intensities are much greater than those anticipated by the…
A novel AlAs/n-GaAs superlattice structure, in which the GaAs midlayers are selectively doped with Si, has been designed as an electron supplying layer for two-dimensional electron gas (2DEG) systems to obtain a high sheet carrier concentration, using a simple Kronig–Penney model calculation. The optimized structure i…
The pseudo-binary compounds Gd(Fe 1- x Mn x ) 2 have been investigated. The crystal structures are C-15 for x ≤0.2 and x ≥0.9, X-structure for 0.4≤ x ≤0.7 and mixture (C-15 and X-structure) for x =0.3 and 0.8, respectively. The measurements of X-ray diffraction, magnetic measurement, NMR and Mössbauer effect were carr…
The results of an investigation of thermal effects on the fluorescence spectra of Ti3+ in sapphire are presented. As-grown samples synthesized by the Czochralski method were found to exhibit a fluorescence band characteristic of Ti4+. After thermal annealing this band was greatly reduced and the Ti3+ fluorescence was…
The bonding in Fe2(CO)9 is analyzed using an SCF wave function for a large basis set. There is no direct Fe–Fe metal–metal bond. The bridging CO’s hold the two Fe(CO)3 fragments together by σ donation into the empty Fe–Fe dπ orbital and metal donation from the dπ* orbital into the CO 2π* orbital. The bonding of the te…
Recent work has indicated that the single-scattering theory of x-ray absorption may be valid down to much closer to the edge than previously thought. It is in this region that the plane-wave approximation used in the standard extended x-ray-absorption fine structure analysis breaks down. Using a simple reformulation,…
Nitrogen-doping and -implantation studies reveal a new photoluminescence spectrum in silicon with a no-phonon transition at 0.746 eV. The line exhibits $^{14}\mathrm{N}$${,}^{15}$N and $^{12}\mathrm{C}$${,}^{13}$C isotope splittings showing that single nitrogen and carbon atoms are incorporated in the defect. Zeeman m…
The electrical resistivity of layerd crystalline GeSe has been investigated up to a pressure of 100 kbar and down to liquid-nitrogen temperature by use of a Bridgman anvil device. A pressure-induced first-order phase transition has been observed in single-crystal GeSe near 6 GPa. The high-pressure phase is found to be…
The Mn-intercalated transition metal dichalcogenides Mn 1/4 NbS 2 and Mn 1/4 TaS 2 have been found to be easy-plane type ferromagnets from the magnetization curves, while the magnetization curve of Mn 1/4 NbSe 2 shows a spin flopping behavior, suggesting a helical spin structure along the c -axis. The valency of Mn io…